A contractor estimates that a job will earn him Rs. 8,400. His estimate covers material, labour and 5% profit. The cost of material and labour is in the ratio of 3:7. When the contractor begins his job, he discovers that the cost of material has increased by 10% and the labour by 15%. Calculate his loss per cent.

Profit and loss are used to determine the price of a commodity and to understand how profitable a business is. 

In business, profit is the difference between a business's income and expenses. A profit and loss statement (P&L) is a summary of a business's income and expenses over a specific period. It's also called an income statement. 
Profit is the amount gained by selling a product for more than its cost price. Loss is the amount incurred by selling a product for less than its cost price. 
The profit formula is SP - CP and the loss formula is CP - SP.